fixes an old ARC bug: the produced copy/sink operations don't copy the hidden type field for objects with enabled inheritance; fixes #19205 [backport:1.6] (#19232)

compiler/ast.nim

@@ -673,7 +673,7 @@ type
     mSwap, mIsNil, mArrToSeq,
     mNewString, mNewStringOfCap, mParseBiggestFloat,
     mMove, mWasMoved, mDestroy, mTrace,
-    mDefault, mUnown, mFinished, mIsolate, mAccessEnv, mReset,
+    mDefault, mUnown, mFinished, mIsolate, mAccessEnv, mAccessTypeField, mReset,
     mArray, mOpenArray, mRange, mSet, mSeq, mVarargs,
     mRef, mPtr, mVar, mDistinct, mVoid, mTuple,
     mOrdinal, mIterableType,

compiler/ccgexprs.nim

@@ -1741,6 +1741,13 @@ proc genGetTypeInfoV2(p: BProc, e: PNode, d: var TLoc) =
     # use the dynamic type stored at offset 0:
     putIntoDest(p, d, e, rdMType(p, a, nilCheck))
 
+proc genAccessTypeField(p: BProc; e: PNode; d: var TLoc) =
+  var a: TLoc
+  initLocExpr(p, e[1], a)
+  var nilCheck = Rope(nil)
+  # use the dynamic type stored at offset 0:
+  putIntoDest(p, d, e, rdMType(p, a, nilCheck))
+
 template genDollar(p: BProc, n: PNode, d: var TLoc, frmt: string) =
   var a: TLoc
   initLocExpr(p, n[1], a)
@@ -2449,6 +2456,7 @@ proc genMagicExpr(p: BProc, e: PNode, d: var TLoc, op: TMagic) =
   of mMove: genMove(p, e, d)
   of mDestroy: genDestroy(p, e)
   of mAccessEnv: unaryExpr(p, e, d, "$1.ClE_0")
+  of mAccessTypeField: genAccessTypeField(p, e, d)
   of mSlice: genSlice(p, e, d)
   of mTrace: discard "no code to generate"
   else:

compiler/ccgtypes.nim

@@ -583,7 +583,7 @@ proc getRecordDesc(m: BModule, typ: PType, name: Rope,
 
   if typ.kind == tyObject:
     if typ[0] == nil:
-      if (typ.sym != nil and sfPure in typ.sym.flags) or tfFinal in typ.flags:
+      if lacksMTypeField(typ):
         appcg(m, result, " {$n", [])
       else:
         if optTinyRtti in m.config.globalOptions:

compiler/liftdestructors.nim

@@ -941,6 +941,12 @@ proc symPrototype(g: ModuleGraph; typ: PType; owner: PSym; kind: TTypeAttachedOp
   incl result.flags, sfFromGeneric
   incl result.flags, sfGeneratedOp
 
+proc genTypeFieldCopy(c: var TLiftCtx; t: PType; body, x, y: PNode) =
+  let xx = genBuiltin(c, mAccessTypeField, "accessTypeField", x)
+  let yy = genBuiltin(c, mAccessTypeField, "accessTypeField", y)
+  xx.typ = getSysType(c.g, c.info, tyPointer)
+  yy.typ = xx.typ
+  body.add newAsgnStmt(xx, yy)
 
 proc produceSym(g: ModuleGraph; c: PContext; typ: PType; kind: TTypeAttachedOp;
               info: TLineInfo; idgen: IdGenerator): PSym =
@@ -980,6 +986,10 @@ proc produceSym(g: ModuleGraph; c: PContext; typ: PType; kind: TTypeAttachedOp;
       fillStrOp(a, typ, result.ast[bodyPos], d, src)
     else:
       fillBody(a, typ, result.ast[bodyPos], d, src)
+      if tk == tyObject and a.kind in {attachedAsgn, attachedSink, attachedDeepCopy} and not lacksMTypeField(typ):
+        # bug #19205: Do not forget to also copy the hidden type field:
+        genTypeFieldCopy(a, typ, result.ast[bodyPos], d, src)
+
   if not a.canRaise: incl result.flags, sfNeverRaises
   completePartialOp(g, idgen.module, typ, kind, result)
 

compiler/types.nim

@@ -1705,3 +1705,6 @@ proc isCharArrayPtr*(t: PType; allowPointerToChar: bool): bool =
       result = allowPointerToChar
     else:
       discard
+
+proc lacksMTypeField*(typ: PType): bool {.inline.} =
+  (typ.sym != nil and sfPure in typ.sym.flags) or tfFinal in typ.flags

tests/arc/tarcmisc.nim

@@ -30,6 +30,7 @@ ok
 true
 copying
 123
+42
 closed
 destroying variable: 20
 destroying variable: 10
@@ -482,3 +483,17 @@ method testMethod(self: BrokenObject) {.base.} =
 
 let mikasa = BrokenObject()
 mikasa.testMethod()
+
+# bug #19205
+type
+  InputSectionBase* = object of RootObj
+    relocations*: seq[int]   # traced reference. string has a similar SIGSEGV.
+  InputSection* = object of InputSectionBase
+
+proc fooz(sec: var InputSectionBase) =
+  if sec of InputSection:  # this line SIGSEGV.
+    echo 42
+
+var sec = create(InputSection)
+sec[] = InputSection(relocations: newSeq[int]())
+fooz sec[]